1. Field of the Invention
The present invention relates to the field of fasteners and, more particularly, to tamper-resistant fasteners (e.g., bolts) and to fasteners requiring tightening to a precise torque.
2. Related Art
In many instances it is necessary to prevent unauthorized intrusion or disassembly of a product in order to prevent theft or injury. Use of such fasteners on medical equipment ensures that unskilled individuals will not attempt adjustments. Use on cable set-top boxes prevents tampering with the electronics within. Use on public structures such as playground equipment, picnic benches, and on restroom fixtures prevents theft and disassembly-type vandalism.
While it is impossible to stop a determined thief, most applications of tamper-resistant technology require only that access be made very difficult unless a special tool is used. To accomplish this, prior designs modified the heads of commonly used bolts and screws to disallow removal using ordinary wrenches and screwdrivers. Once modified, the head of the fastener will only mate with a tool that incorporates the analog of the modified head. It is apparent that this method of creating a tamper-resistant fastener relies on the relative scarcity of installation tools.
Modifying the head of a fastener to incorporate offset holes, cam-like pockets or steps proves difficult to manufacture due to the high tolerances that must be held. As a result, the price of tamper-resistant fasteners is high. By necessity, the installation tools are encumbered with a complex, and often quite sharp or dangerous, tool tip. This becomes a hazard during installation when torque is applied and the tool tip cams out of the fastener head and skids across the articles being joined. This situation is highly undesirable, dangerous and happens far too often using existing designs. Cam-out is a major problem for manufacturers that focus on product quality such as the auto industry.
A further problem with standard and tamper-resistant fasteners relates to the inability to accurately torque down the fastener during install. Installation torque is dependent upon many factors and is often critical to holding an assembly together as designed. The most common method for applying a set amount of torque is to use a tool that incorporates a clutch that releases when a set rotational force is exceeded. Often these tools use a spring as the torque reference for the clutch. Stretching or compression of the spring over time introduces inaccuracies to the torque measurement. Electronic and manual installation tools utilize the same general principle and suffer the same inaccuracies. Electronic systems are generally used in the automotive and aircraft industries on, for example, door latches and components that may affect the safety of users/passengers.
What is needed is a better fastener and fastening system and method. Moreover, it would be extremely valuable for a fastener to incorporate a single use torque setting feature into its design. Installation tool maintenance and calibration would no longer be an issue if the fastener included a feature that would not allow over torqueing.